1. Field of the Invention
The present invention relates to an electronic equipment arrangement; more specifically, a cylindrical backplane for electronic circuit cards.
2. Description of the Related Art
FIG. 1 illustrates a prior art backplane arrangement. Backplane 10 comprises upper connectors 12 and lower connectors 14. Contacts 16 within each connector pair, 12 and 14, mate with contacts on the surface of a circuit card. The contacts on the surface of the circuit card are positioned near the edge of the card so that they make contact with electrical contacts 16 when the card edge is inserted into the connector. Backplane 10 typically includes conductors that connect corresponding contacts on each of the connectors to create a bus structure. For example, contacts 18, 20, 22 and similarly positioned contacts of connectors 12, are connected through the conductors of backplane 10. This arrangement provides a convenient busing connection between circuit cards that are designed to meet a particular input/output standard. For example, if contacts 18, 20, 22 and the corresponding contacts of connectors 12, are designated as a power contact, all circuit cards designed to mount to backplane 10 have a power contact that mates with the power contacts of connector 12 when the card is inserted into the connector.
Unfortunately, with today's high-speed circuitry, the horizontal length of backplane 10 has a finite limit, for example, ISA (Industry Standard Architecture) backplanes are limited to approximately 22 inches. If the horizontal dimension of the backplane is made larger, propagation delays and transmission line effects interfere with signal transmissions between cards that are at the far ends of the backplane. As a result, the number of circuit cards that can be mounted to backplane 10 is limited to the of circuit cards that can be mounted within a length of approximately 22 inches. Unfortunately, the circuit cards cannot be mounted too close to each other because of cooling requirements. If the cards are mounted too closely together, cooling air does not circulate sufficiently and results in circuit card overheating. Typically, 0.8 inches is provided between the circuit cards in a ISA backplane. As a result, only 25 circuit cards are mounted in a backplane such as backplane 10. This limits the amount of high-speed circuitry that can be positioned within a single backplane, and thereby limits the amount of functionality that can be provided.